1. Field of the Invention
The present invention relates to an optical device, notably for a motor vehicle, such as a lighting and/or signaling device that notably has a photometric function that is useful for road travel, enabling the vehicle to be seen by other vehicles or enabling the driver of the vehicle to see outside.
2. Description of the Related Art
It is known practice, notably from the document DE 10 2007 018 985, which document is incorporated herein by reference and made a part hereof, to use surface light sources, in particular an organic light-emitting diode, as light source of a motor vehicle optical device, in the case of DE 10 2007 018 985, which document is incorporated herein by reference and made a part hereof, a motor vehicle signaling device. Although a light source of organic light-emitting diode type makes it possible to provide an extremely uniform light, it has many drawbacks:
Firstly, the organic light-emitting diodes, also called OLEDs, these days comprise small molecules, because they are more effective and better suited to producing a signaling function in a limited space, for example a rear wing of a vehicle. However, these molecules have to be protected from water and oxygen molecules, which is done using glass plates. The OLEDs used to produce a signaling function therefore comprise a protective glass plate in contact with the emitting layer. The glass plates greatly limit the possible forms of the organic light-emitting diodes. The OLEDs therefore need to have planar surfaces or at the very least regular surfaces and they cannot therefore consist of a screen that has any awkward surface as a standard lens of a lighting and/or signaling device of a motor vehicle. This therefore poses design problems.
Next, the luminance supplied by an organic light-emitting diode of current technology is not sufficient to ensure certain signaling functions (such as the “town signaling”, “braking signaling” and “boosted braking signaling” signaling functions). An organic light-emitting diode of current technology typically supplies a luminance of 1000 Cd/m2 whereas, to ensure the abovementioned functions, a luminance of 5000 to 10 000 Cd/m2 would be needed. Nevertheless, a new organic light-emitting diode technology makes it possible to greatly increase the emission directivity of the diode in the direction perpendicular to its emitting surface. Thus, without increasing the emittance of the diode, the luminance can be greatly increased, for example by a factor of 10, to reach approximately 10 000 Cd/m2. However, an organic light-emitting diode of this technology is highly directive. Consequently, it presents, in addition to the drawback mentioned previously, that of having to be oriented in the longitudinal axis of the vehicle or, more generally, in the direction in which it has to emit the light. This therefore poses design problems, notably bulk and design problems.
Consequently, the use of an organic light-emitting diode in a lighting and/or signaling device of a motor vehicle is valid only if this surface is a regular surface. It is then possible to produce a lighting or signaling device by depositing an organic light-emitting diode on a flexible substrate. The efficiency of such a technology is very low in comparison to the technologies in which the diodes are deposited on a flat glass substrate.
Also known from the document DE 10 2007 018 986, which document is incorporated herein by reference and made a part hereof, is a lighting device for a passenger compartment of a motor vehicle comprising:
an assembly of organic light-emitting diodes onto which are glued a first optical element, and
a second optical element.
Also known from the documents DE 202 07 799 and EP 1 485 959, which is equivalent to U.S. Patent Publication 2005/0117347, which are incorporated herein by reference and made a part hereof, are motor vehicle signaling devices comprising an organic light-emitting diode covered by an optical element comprising a spatial repetition of a pattern in order to improve the efficiency of the diode by virtue of the fact that the rays are less easily trapped in total reflection and can thus more easily leave the transparent substrate. This technology is of interest only if the optical element is glued to the substrate, in other words if the optical element is glued onto a plane. Such signaling devices do not make it possible to resolve the problems mentioned above.
Also known from the document FR 2 926 677, which is equivalent to U.S. Patent Publication 2011/0079772, which is incorporated herein by reference and made a part hereof, is an organic light-emitting diode device emitting a light beam having a strong directivity. Such an organic light-emitting diode comprises, between its two electrodes, different layers, notably a light-emitting layer, a layer promoting the transfer of the electrons to the emitting layer and a layer promoting the transfer of the holes to the emitting layer. The assembly of these layers constitutes a microcavity whose thickness is engineered to create an optical resonance. The result of such a structure is an emission of a light beam that exhibits a strong directivity.